The polyphenylene ethers are known and described in numerous publications including Hay, U.S. Pat. No. 3,306,874 and 3,306,875 and Stamatoff 3,257,357 and 3,257,358. The high molecular weight polyphenylene ethers are high performance engineering thermoplastics possessing relatively high melt viscosities and softening points--i.e., in excess of 275.degree. C., and are useful for many commercial applications requiring high temperature resistance including formation of films, fibers and molded articles.
Although they have the above-described desirable properties, it is also known that certain properties of the polyphenylene ether resins are undesirable for some commercial uses. For example, parts molded from the polyphenylene ethers are somewhat brittle due to poor impact strength. In addition, the relatively high melt viscosities and softening points are considered a disadvantage for many uses. Films and fibers can be formed from polyphenylene ether resins on a commercial scale using solution techniques, but melt processing is commercially unattractive because of the high temperatures required to soften the resin and the problems associated therewith such as instability, discoloration and the requirement for specially designed process equipment to operate at elevated temperatures. Molded articles can be formed by melt processing techniques, but, again, the high temperatures required are undesirable.
It is known in the art that properties of the polyphenylene ether resins can be materially altered by blending them with other resins. For example, in commonly-assigned patent, U.S. Pat. No. 3,361,851, a polyphenylene ether composition comprising a polyphenylene ether blended with a polyolefin is disclosed. The polyolefin is added to improve impact strength and resistance to aggressive solvents. In a second commonly assigned patent, Cizek, U.S. Pat. No. 3,383,435, there are provided means for simultaneously improving the melt processability of the polyphenylene ether resins while simultaneously up-grading many properties of polystyrene homopolymer and random copolymer resins. The invention of the Cizek patent is based upon the discovery that the polyphenylene ether resins and such polystyrene resins, including rubber modified polystyrene resins, are combinable in all proportions and result in compositions having many properties improved over those of either of the components. When polyethylene is incorporated in polyphenylene ether or in compositions thereof with styrene resins, melt flow and physical properties are markedly improved. The amount of polyolefin which can be incorporated is limited, however, to about 5 parts per hundred of resin, due to excessive delamination and accompanying brittleness.
It has also been disclosed, see commonly assigned U.S. Pat. No. 3,994,856, and application Ser. No. 387,588, filed Aug. 13, 1973, abandoned in favor of application Ser. No. 826,196 filed Aug. 19, 1977 that an elastomeric block copolymer of a vinyl aromatic compound (A) and (A).sup.1 and a conjugated diene (B), of the A-B-A.sup.1 type, A and A.sup.1 being the same or different, and the molecular weight of the center block being higher than that of the terminal blocks, or a hydrogenated derivative thereof, will impart unexpectedly high impact strengths and chemical resistance properties both to polyphenylene ether resins and compositions of polyphenylene ether resins and polystyrene homopolymer and random copolymer resins. These applications are incorporated herein by reference.
It has now been discovered that much higher amounts of polyolefin can be incorporated if a block copolymer is also incorporated in the composition. Most unexpected is a tremendous synergistic increase in Izod impact strength following use of the combination of polyolefin and block copolymer. A small amount of a plasticizer provides further enhancement of impact strength.